High modulus metallic component for high vibratory operation

ABSTRACT

A high modulus component, such as an aircraft engine turbine blade, is formed from a base metal that has a high modulus crystallographic orientation that is aligned with the primary, i.e. radial, direction of the turbine blade. The base metal is Ni, Fe, Ti, Co, Al, Nb, or Mo based alloy. Alignment of a high modulus direction of the base metal with the primary direction provides enhanced high cycle fatigue life.

This invention was made with government support under Contract No.N00019-02-C-3003 awarded by the Department of the Navy. The governmenttherefore has certain rights in this invention.

BACKGROUND OF THE INVENTION

This invention relates to a metallic component such as an aircraftengine turbine blade that is formed with a high modulus orientation of ametal being aligned in the radial, i.e. primary, direction of theturbine blade.

Machines that utilize high speed components, such as an aircraft engine,produce high frequency vibrations. The high frequency vibrations aretypically on the order of kilohertz and impose a variety of fluctuatinghigh cycle fatigue stresses on the high speed components of the machine.Often, the limiting factor in the life of a high speed component is highcycle fatigue stress. While the present invention is described in thecontext of a turbine blade, it will be recognized that the invention isnot so limited.

Conventionally, the life of high speed components, such as a turbineblade employed in aircraft engine, is enhanced by designing thecomponent to resist or minimize the imposed stresses. This involvesdesigning the turbine blade so that the natural vibrational frequenciesdo not match the vibrational frequencies produced by the high speeds. Aturbine blade designed in this way minimizes the stress amplitude byavoiding a resonant effect that amplifies the stresses. It is not alwayspossible however, to design a blade that has adequately differentnatural vibrational frequencies from those produced by the high speedmotion.

Another turbine blade design approach attempts to dampen the vibrationsat critical locations on the blade. Various damping designs, such asfriction damping or the application of damping coatings, are availableto help reduce the stress amplitude at the critical locations. Dampingis often expensive, involves highly complex analysis andexperimentation, and may impair the performance of the turbine blade.

Accordingly, a metallic component, such as aircraft engine turbineblade, that provides enhanced high cycle fatigue life is needed.

SUMMARY OF THE INVENTION

In general terms, this invention is a directionally solidified metalliccomponent, such as an aircraft engine turbine blade that is formed froma base metal that has a high modulus crystallographic orientationaligned with the radial, i.e. primary, direction of the turbine blade.

In one example, the engine turbine blade is formed from a single crystalof Ni based alloy and the <111> crystallographic direction is alignedwith the primary direction of the turbine. Alternatively, the engineturbine blade is formed from an alloy of Fe, Ti, Al, Co, Nb, or Mo and ahigh modulus direction of the alloy is aligned with the primarydirection of the turbine blade.

In another example, a high modulus direction of the base metal thatforms the engine turbine blade is aligned with the primary direction ofa columnar grain structure and the primary direction of the columnargrain structure is aligned with the primary direction of the turbineblade.

In another example, the engine turbine blade is formed from a Ni basedalloy and the <112> high modulus crystallographic direction is alignedwithin a cone of about ten degrees of the primary direction of theturbine blade.

In another example, the engine turbine blade is formed from a Ni basedalloy and the <123> high modulus crystallographic direction is alignedwithin a cone of about ten degrees of the primary direction of theturbine blade.

In another example, the engine turbine blade is formed from a Ni basedalloy and the <110> crystallographic direction is aligned to withinabout ten degrees of the primary direction.

In another example, the Ni base metal that forms the engine turbineblade that has a high modulus direction aligned with the primarydirection is a Ni superalloy.

In another example, the engine turbine blade turbine blade is heattreated to recrystallize the base metal with a high modulus directionaligned with the primary direction of the turbine blade.

In another example, the engine turbine blade that has a high modulusdirection aligned with the primary direction is in an aircraft engine.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an aircraft engine.

FIG. 2 is a schematic cross sectional view of an aircraft engine turbineblade;

FIG. 3 is a sketch of a single crystal unit of a base metal;

FIG. 4 is a microscopic sketch of an equiaxed Ni metal portion;

FIG. 5 is a microscopic sketch of an anisotropic Ni metal portion;

FIG. 6 is a microscopic sketch of a single crystal Ni metal portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a cross sectional schematic view of an aircraft engine 2.The aircraft engine 2 includes an engine casing 3 that houses a fan 4that is in fluid communication with a compressor 5. The compressor 5includes impellers 6 that pressurize air in the aircraft engine 2. Theimpellers 6 are attached to a rotatable shaft 7 that rotates around axis8. When the shaft 7 rotates, the impellers 6 rotate. A combustor 9 is influid communication with pressurized gas that exits from the compressor5. The combustor 9 combusts the pressurized gas. A turbine 10 receivesthe combusted pressurized gas and converts it into energy that is usedto rotate the shaft 7 and power the compressor 5. The turbine 10includes a rotor 11 that is attached to the shaft 7, and turbine blades13 that are attached to the rotor 11.

The axial direction 18 is approximately the same direction of the axis11 (referring to FIG. 1) around which the turbine blade 13 rotates. Theprimary direction 16 is substantially perpendicular (i.e. radialrelative to the axis 11 about which the turbine blade 13 rotates—seeFIG. 1). A significant amount of fatigue stress occurs in the primarydirection 16 due to the high speed rotation of the turbine blade 13around the axis 11.

Referring to FIG. 2, the turbine blade 13 has base portion 14 and tipportion 15. The turbine blade 13 further includes an associated primarydirection 16 that extends from the base portion 14 to the tip portion 15and a substantially perpendicular axial direction 18. The turbine blade13 has a dimension L₁ in the primary direction and a dimension W₁ in theaxial direction. The dimension L₁ is greater than the dimension W₁. Thatis, the turbine blade 13 has a L₁ to W₁ aspect ratio greater than one.The primary direction 16 is defined as the direction of the greaterdimension L₁ in the turbine blade 13, or the greater dimension of anycomponent having an aspect ratio that is greater than one.

The turbine blade 13 is formed from a base metal. A base metal is theprimary metal of an alloy and may include substantial amounts ofalloying elements. All alloys and metals are crystalline and thereforehave an associated crystal structure. The example in FIG. 3 refers to asketch of a single crystal unit of the crystal structure of a base metalused, for example, to form the aircraft engine turbine blade 13. Thesingle crystal unit 19 has known crystallographic directions, forexample the <100> direction represented by the line 20, <110>represented by the line 21, <111> represented by the line 22, <112>represented by the line 24, and <123> represented by the line 26. Forengineering purposes, the crystallographic direction refers to theapproximate coordinate direction within about a ten degree cone angle 28of the exact direction.

Each crystallographic direction also has an associated elastic modulusand, if at least one of the crystallographic directions has an elasticmodulus that is not equal to the elastic moduli in the othercrystallographic directions, the single crystal unit 19 is anisotropicwith respect to elastic modulus.

Inside the aircraft engine 2, the turbine blades 13 operate at highrotational speeds as the combusted pressurized gas from the combustor 9expands. The high speeds cause vibrations in the aircraft engine 2 andimpose high frequency fatigue stresses on the turbine blades 13, i.e.high cycle fatigue.

In one example, a Ni based alloy is the base metal. At room temperature,in the <100> crystallographic direction the Ni based alloy has anelastic modulus of about 20 Mpsi, in the <110> crystallographicdirection an elastic modulus of about 34 Mpsi, and in the <111>crystallographic direction an elastic modulus of about 44 Mpsi. The<100> is a low modulus direction because it has a lower modulus thananother direction (here either the <110> or <111> directions) and the<111> is a high modulus direction because it has a higher modulus thanat least one other direction (<110> or <100>). For the single crystalunit 19, the Ni based alloy is anisotropic.

Generally, despite anisotropy, an article or component formed from ananisotropic base metal will not always exhibit anisotropic propertiessuch as for elastic modulus.

For example, FIG. 4 shows a microscopic sketch of a known equiaxed Nibased alloy portion 30 of an article that was solidified in anuncontrolled manner during forming of the article, e.g. without a heatgradient. The equiaxed Ni based alloy portion 30 is comprised of grains32. Each grain 32 has a crystallographic orientation 34 corresponding toa crystallographic direction such as referred to in FIG. 1 for example.The crystallographic orientations 34 of the grains 32 are randomlyoriented, i.e. equiaxed. Therefore, the elastic modulus and otherproperties of the equiaxed Ni based alloy portion 30 are the same in alldirections.

FIG. 5, however, shows an anisotropic Ni based alloy portion 36 of anarticle or component that was solidified in a controlled manner duringforming, e.g. with a controlled heat gradient. The anisotropic Ni basedalloy portion 36 is comprised of a columnar grain 38 structure having aprimary direction 40 and a transverse direction 42. Each columnar grain38 has a crystallographic orientation 44 that is aligned in the primarydirection 40. The elastic modulus and other properties of theanisotropic Ni based alloy portion 36 are therefore different in theprimary direction 40 than in the transverse direction 42.

As shown in FIG. 6, a single crystal Ni based alloy portion 46 alsoexhibits anisotropic properties. The single crystal Ni based alloyportion 46 was solidified in a controlled manner using the known processof seeding, for example. The single crystal Ni based alloy portion 46contains a single crystal 48 structure having a primary direction 50 andtransverse direction 52. The single crystal 48 has a crystallographicorientation 54 that is aligned in the primary direction 50. Theproperties of the single crystal Ni based alloy portion 48 are thereforedifferent in the primary direction 50 than in the transverse direction52.

As referred to for FIG. 5, the anisotropic Ni based alloy portion 36 wassolidified in a controlled manner during forming. For example, the knownprocess of investment casting may yield columnar grain 38 structurebecause of a cooling gradient during the solidification process. Thisprocess results naturally in the columnar grains 38 having acrystallographic orientation 44 in the <100> low modulus direction (i.e.the primary direction 46). Since Ni based alloy metal has an elasticmodulus of about 20 Mpsi in the <100> direction, the anisotropic Nibased alloy portion 36 has an elastic modulus of about 20 Mpsi in theprimary direction 40.

As referred to for FIG. 6, the single crystal Ni based alloy portion 46was solidified in a controlled manner during forming. For example, theknown process of investment casting using a seed may be used to producethe single grain 48. This process results naturally in the single grain48 having a crystallographic orientation 54 in the <100> low modulusdirection (i.e. the primary direction 46). Since Ni based alloy has anelastic modulus of about 20 Mpsi in the <100> direction, the singlecrystal Ni based alloy portion 46 has an elastic modulus of about 20Mpsi in the primary direction 50.

In one preferred example, a Ni based alloy is used as the base metalforming the turbine blade 13 and has the <111> crystallographicdirection aligned with the primary direction 16. Ni based alloy ispreferred, but alloys of Fe, Co, Mo, Ti, Nb, and Al could alternativelybe used. As is known, a high modulus direction for cubic crystalstructured metals, such as Ni, is the <111> direction, but one skilledin the art would recognize the high modulus directions in base metalshaving other crystal structures as well as other high modulus directionsin cubic crystal structured metals. It should be understood that one ofordinary skill in the art who has the benefit of this disclosure wouldrecognize the applicability of aligning a high modulus direction with aprimary direction to articles other than an aircraft turbine blade suchas, but not limited to, industrial gas turbines, aircraft compressorblades, and generally any high speed component having an aspect ratiogreater than one.

In another example the base metal of the turbine blade 13 has a columnargrain 38 structure. A high modulus direction of the base metal isaligned with the primary direction 40 of the columnar grains 38. Theprimary direction 40 of the columnar grains 38 is aligned with theprimary direction 16 of the turbine blade 13.

In another preferred example, the base metal has a single grain 48structure. A high modulus direction of the base metal is aligned withthe primary direction 50 of the single grain 48. The primary direction50 of the single grain 48 is aligned with the primary direction 16 ofthe turbine blade 13.

In another example a Ni based alloy forms the aircraft engine turbineblade 13 and the <112> high modulus direction is aligned to within abouta ten degree cone angle 28 of the primary direction 16.

In another example a Ni based alloy forms the aircraft engine turbineblade 13 and the <123> high modulus direction is aligned to within abouta ten degree cone angle 28 of the primary direction 16.

In another example a Ni based alloy forms the aircraft engine turbineblade 13 and the <110> high modulus direction is aligned to within abouta ten degree cone angle 28 of the primary direction 16.

In another example, the Ni base metal is a known superalloy. Thecomposition of the superalloy is 1-16% Cr, 0-3% Mo, 3-13% W, 0-8% Re,0-14% Ta, 3-7% Al, 0-20% Co, 0-0.1% C, 0-0.02% B, 0-0.1% Zr, 0-2% Hf,0-2% Nb, 0-1% V, 0-2% Ti, 0-10% (Ru+Rh+Pd+Os+Ir+Pt), 0-0.25% Y, and thebalance Ni. In this composition 0-10% (Ru+Rh+Pd+Os+Ir+Pt) means amixture of any or all of the six elements but not exceeding 10%. Thiscomposition is known in the aircraft industry to be adequate for formingturbine blades that have the low modulus <100> direction aligned withthe primary direction of the blade but not for any high modulusdirections such as <123>, <112> and <111>. One specific superalloy forthe high modulus turbine blade 13 is of the composition 5.0% Cr, 10% Co,2.0% Mo, 6.0% W, 3.1% Re, 5.6% Al, 9.0% Ta, 0.1% Hf, and the balance Ni.Another specific superalloy for the high modulus turbine blade 13 is ofthe composition 2.0% Cr, 16.5% Co, 2.0% Mo, 6.0% W, 6.0% Re, 3.0% Ru,5.65% Al, 0.15% Hf, 0.004% B, 0.05% C, and the balance Ni.

An aircraft engine turbine blade 13 that has a high modulus directionaligned in the primary direction 16 is particularly well suited to lowerstresses imposed by high cycle engine vibration, i.e. high cyclefatigue. In one example, the engine turbine blade 13 is formed with a Nibased alloy and has the <111> direction aligned with the primarydirection 16. The engine turbine blade 13 has a higher natural vibrationfrequency than a turbine blade that has the <100> direction aligned withthe primary direction 16. This results in a reduction in stressamplitude from high cycle vibrations and thus enhanced high cyclefatigue life.

An aircraft engine turbine blade 13 that has a high modulus directionaligned in the primary direction 16 is counter to the current practicein the industry. Current practice utilizes aircraft engine turbines thathave the low modulus direction <100> aligned with the primary direction16 because the investment casting forming process naturally produces the<100> direction aligned with the primary direction 16. Moreover, the lowmodulus direction <100> was thought to be the best design because itexhibits other favorable properties such as thermal mechanical fatigueresistance.

A known investment casting method of forming can be utilized to producean aircraft engine turbine blade 13 that has a high modulus directionaligned in the primary direction 16. Generally, investment castinginvolves pouring a molten metal into a mold and cooling the mold in acontrolled manner so that that the molten metal solidifies in acontrolled manner. This processing method can be used to align a highmodulus direction with the primary direction 16. Those skilled in theart of metal forming would recognize the processing steps required toproduce an engine turbine blade according to the invention. That is, aturbine blade having high modulus properties is novel and inventive,however, a worker of ordinary skill in the art would know of theinvestment casting process to produce it.

A seed may also be used in the investment casting process to produce acomponent with a single crystal structure rather than a columnar grainstructure. For example, a <111> oriented Ni seed would be used to inducesingle crystal growth in the <111> direction for investment casting asingle crystal Ni base metal turbine blade 13 that has the <111>direction aligned with the primary direction 16. It should be understoodthat, while a turbine having high modulus properties is novel andinventive, the methods of investment casting and seeding are known tothose of ordinary skill in the art of metal forming, the details ofwhich are hereby incorporated by reference.

A turbine blade 13 that has a high modulus direction aligned in theprimary direction 16 can also be formed by a known machining process. Inthe machining process, the aircraft engine turbine blade 13 is machinedfrom a cast ingot. The ingot is cast, for example, with a <100>direction. The primary direction 16 of the turbine blade 13 is machinedat approximately a fifty-four degree angle to the ingot <100> direction.This results in the <111> high modulus direction being aligned with theprimary direction 16.

The turbine blade 13 that has a high modulus direction aligned in theprimary direction 16 can also be formed by the known process of tiltingthe component during casting. During solidification, the aircraft engineturbine blade 13 may be tilted at a particular angle relative to thedirection of a cooling gradient so that the high modulus direction isaligned with the primary direction 16.

The turbine blade 13 that has a high modulus direction aligned in theprimary direction 16 can also be formed by the known process ofrecrystallization. Recrystallization involves heat treating a cast orwrought turbine blade to form new grains from the grains that alreadyexisted before the heat treatment. The new grains have a high modulusdirection aligned with the primary direction 16.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology used is intended to be in the natureof words of description rather than of limitation. Obviously, manymodifications and variations of the present invention are possible inlight of the above teachings. It is, therefore, to be understood thatwithin the scope of the appended claims the invention may be practicedotherwise than as specifically described.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

1. A high modulus turbine blade comprising: a base portion and a tipportion; a primary direction that extends from said base portion to saidtip portion; and said turbine blade being formed of a base metal thathas a crystallographic orientation, said crystallographic orientationhaving a high modulus direction, wherein said high modulus direction isaligned with said primary direction, and wherein said base metal is anickel-based alloy composition comprising 2.0% Cr, 16.5% Co, 2.0% Mo,6.0% W, 6.0% Re, 3.0% Ru, 5.65% Al, 0.15% Hf, 0.004% B, 0.05% C, and abalance Ni.
 2. The turbine blade as recited in claim 1, wherein saidhigh modulus direction is aligned to within a cone of about ten degreesof said primary direction.
 3. The turbine blade as recited in claim 1,wherein said base metal comprises recrystallized grains.
 4. The turbineblade as recited in claim 1, wherein said high modulus direction iswithin about ten degrees of the <111> crystallographic direction.